The present invention relates to a thermal development apparatus as well as a thermal development method in which an image is formed by feeding a thermally developable material on the outer circumferential surface of a drum and heating it.
A thermal development apparatus is developed in which by successively feeding a sheet of thermally developable material onto the outer circumferential surface of a heated drum, the thermally developable material undergoing a thermal reaction so that an image formed as a latent image will be visible (refer to Japanese Patent Publication Open to Public Inspection under PCT Application No. 10-500497). Such a thermal development apparatus is constituted in such a manner that sheets of thermally developable material are fed onto the outer circumferential surface of a drum which rotates at a constant speed; after the drum rotates a specified angle, while the material is held on the surface, the thermally developable material, which has been heated, is peeled from the outer circumferential surface of the drum; at the same time, another sheet of thermally developable material is fed onto the outer circumferential surface of the drum; and thus, sheets of thermally developable material can be efficiently heated.
Such a thermal development apparatus has been supposed to be preferable based on the fact that when time TR required for one rotation of the drum is the same as the interval between the time when the leading edge of the sheet of thermally developable material is fed to the drum and the time when the following sheet is fed to the same, the sheets of thermally developable material which are seccessively heated by the drum can be developed under the same conditions, and further, a sheet of thermally developable material catching mechanism can be provided onto the drum.
However, when an apparatus is constructed in the manner as described above, it has been found that after many sheets of thermal developable materials are thermally developed, uneven density results at the leading edge portion as well as the rear edge portion, in the drum rotation direction. In particular, it has also been found that in an apparatus which can thermally develop sheets of thermally developable materials of a plurality of sizes in the drum rotational direction, small-sized sheets of thermally developable material are thermally developed, and thereafter, when a larger-sized sheet of thermally developable material is thermally developed, uneven density results in the center of the image, markedly degrading the image quality of the larger size.
In view of such problems, an object of the present invention is to minimize such uneven density and to make it possible to carry out thermal development to yield high image quality at high speed.
Furthermore, a drum in a thermal development apparatus based on conventional techniques is constructed on the assumption that single-sized sheets of thermally developable material will be employed. It is supposed that the drum is not constructed so as to heat different-sized sheets of thermally developable material. Accordingly, when a drum based on conventional techniques is employed to heat sheets of thermally developable material of different sizes without any adjustment, mismatching between the circumference of the drum and the length of the sheet of thermally developable material in the drum rotation direction occurs. For example, due to the excessively small diameter of the drum, curl and the like tend to result on the sheets.
Furthermore, in view of such problems of conventional techniques, an object of the present invention is to provide a thermal development apparatus as well as a thermal development method which can correspond to different-sized sheets of thermally developable material and can also ensure high image quality, while forming images in a short period of time.